Different elements in Pyongyang, including parts of the military, are capable of taking actions on their own perhaps, without central co-ordination. That is an even more ominous possibility.

He should call President Lee Myung-bak of South Korea to reassure him personally and directly of US support. Then he should call President Hu Jintao of China and express serious concern. He should call Prime Minister Naoto Kan of Japan, as America’s prime ally in the Pacific and given its proximity to the Korean conundrum. He should also call President Dmitry Medvedev of Russia. Hillary Clinton, US secretary of state, should then follow up on these calls and set in motion convening the United Nations Security Council.

he Iranians are maintaining, maybe mendaciously, that they are not seeking nuclear weapons. That is a different kind of challenge in which our response has to be the insistence that they prove their case. The North Koreans, however, are defiant, boasting their nuclear prowess and now openly provocativ

A call from Mr Obama to Mr Hu should be a call between leaders who share a concern. It should not be an American demand, nor an admonition. It should be an affirmation that our respective interests are endangered and so we have a common stake in an effective response.